This invention relates to an adjustable fluid flow regulator, and in particular to an adjustable fluid flow regulator having a finite adjustment limit.
Commercial and Residential gas appliances typically use natural gas or L. P. gas, which are delivered at different pressures. It is desirable to have equipment that can be converted for use with either type of gas, rather than equipment limited in use to just one type of gas. A number of attempts have been made to make an adjustable pressure regulator that is capable of operating within the pressure ranges typical for the two types of gas. Examples of these include Bauman, U.S. Pat. No. 3,747,629; Love, U.S. Pat. No. 4,718,448; Buezis, U.S. Pat. No. 5,435,343; Dalton, U.S. Pat. No. 6,173,775. Most of these devices employ a diaphragm for controlling a valve, a spring for biasing the diaphragm, and a means for varying the spring pressure to adjust the fluid flow regulator.
While the prior adjustable fluid flow regulators are useful for the purposes described, there is still a need to reduce the risk of inadvertent adjustment above the pressure ranges typical for natural gas and L. P. gas, or the specified maximum pressures of the appliance manufacturer.
The present invention relates to an adjustable fluid flow regulator construction that can be converted between two modes of operation, but which restricts accidental or inadvertent adjustment above a predetermined maximum limit. The regulator of the present invention comprises a casing having an inlet and an outlet, a diaphragm-operated valve, and a servo-regulator diaphragm. The servo-regulator diaphragm regulates the passage of a control gas pressure that is applied to one side of the diaphragm that operates the valve. The valve opens and closes as the diaphragm moves in response to pressure changes on either side of the diaphragm. By adjusting the servo-regulator diaphragm, the control gas pressure can be adjusted to control the opening of the valve.
The adjustable fluid flow regulator further comprises a spring for applying pressure against the servo-regulator diaphragm to control the operation of the valve. A first screw and a second screw are both used to adjustably bias the spring against the servo-regulator diaphragm. The second screw, which engages the spring, is adjustably disposed within the first screw. Initially adjusting the regulator involves fully adjusting the first screw to a limit within the regulator, and subsequently adjusting the second screw until the predetermined maximum regulator setting is obtained. Once the maximum setting adjustment is made, the second screw may be restricted from further adjustment in the field by using a non-standard screw head not adjustable by the public, or by a means of covering the screw. Subsequent adjustment would be limited to the first screw and would not exceed the maximum regulator setting established by the limit.